Hitherto, there has been a need to reduce mechanical loss in order to reduce an energy consumption amount in a sliding member such as a cylinder block and a piston used in lubricating oil. Here, a reduction in the friction of the sliding member is examined.
For example, there is known to provide a carbon film such as a diamond-like carbon film (hereinafter, simply referred to as a DLC film) is formed on the surface of the sliding member in order to reduce the friction of the sliding member (for example, see Patent Documents 1 and 2).
When the carbon film is composed on the surface of the sliding member, a conductive workpiece such as a cylinder block and a piston is first disposed in a treatment space maintained in a predetermined vacuum degree. Then, an anode is disposed in the treatment space.
Next, a bias voltage is applied to the anode by setting the workpiece as a cathode while a material gas formed of a hydrocarbon compound such as acetylene is supplied to the treatment space maintained in a predetermined vacuum degree.
In this way, since carbon plasma caused by the material gas such as acetylene is generated along the shape of the surface of the workpiece, the carbon film such as a DLC film may be formed on the surface of the workpiece.
At this time, when the workpiece is a hollow cylindrical member such as a cylinder block, both ends thereof are sealed by a pair of cylindrical sealing members composed of an insulator, and hence the inside of the sealing member and the inside of the workpiece sealed by the sealing member may be formed as the treatment space. In this case, the carbon film is formed on the inner peripheral surface of the hollow cylindrical member.
Further, when the workpiece is a solid member such as a piston, the workpiece is disposed inside a chamber, and hence the inside of the chamber may be formed as the treatment space. In this case, the carbon film is formed on the outer surface of the solid member.